Understanding the relationships between data can be very difficult without drawing pictures. And when that data has a dynamic component and or rich interconnections, the task can't be done without pictures that can be manipulated.An interesting open source Web tool that allows you do just that is TouchGraph (see links below), a Java-based system that draws graphs of node networks such that their connections can be shown at varying levels of detail. The graph can be dragged, any node can be made the focus and nodes and connections can be linked to URLs.You might think of this tool as a less flashy but open source (i.e. nonproprietary) version of Plum Design's ThinkMap.TouchGraph is pretty sophisticated with graph data import being done through XML and very large data sets can be supported. The demos demonstrate both local loading as well as configurations that allow for loading of maps from a Web page.A great demo is the TouchGraph Wiki Browser (see the TouchGraph home page) which displays a graph derived from the interlinking of a wiki (a type of popular online collaborative forum) called Meatball.If you want to download the TouchGraph demos you can do so from the TouchGraph SourceForge home page or the TouchGraph SourceForge files page as the links in the actual home page don't seem to work properly.A word of warning: While this is a great tool beware of a trap that Web designers often seem to fall into - using flashy presentation tools just because they can. There are many useful applications of a tool such as TouchGraph but equally many ways to use it for data that really doesn't benefit from exotic treatment.